Apparatus and method for venous ligation

ABSTRACT

A minimally-invasive surgery apparatus for causing the lumen of a vein to collapse to prevent blood flow through the vein, e.g., a varicose vein or a side branch of the saphenous vein, includes an electrode which is electrically connected to a power source, and the electrode is percutaneously advanced into the vein. Then, the power source is activated to energize the electrode and thus the blood vein until the blood vein sufficiently collapses to block the lumen of the vein. A feedback loop is also provided for sensing electrical impedance of the tissue within the vein being energized and for deenergizing the electrode when the impedance reaches a predetermined value.

This application is a divisional of application Ser. No. 08/183,994,filed Jan. 18, 1994, now U.S. Pat. No. 5,437,664.

FIELD OF THE INVENTION

The present invention relates generally to endoscopic surgical tools.More particularly, the present invention relates to endoscopic apparatusand methods for closing blood vessels. The present inventionparticularly, though not exclusively, relates to endoscopic treatment ofvaricose veins.

BACKGROUND

Certain surgical treatments require the modification or removal of bloodveins from the body. For example, the treatment of varicose veinssometimes requires the varicose veins to be removed from the body in aninvasive, painful, slow-healing, and time-consuming procedure. Also, thesaphenous vein is surgically modified during a procedure, known as insitu saphenous vein bypass, for alleviating conditions caused by reducedblood flow through an occluded femoral artery.

In situ saphenous vein bypass is a procedure in which the saphenous veinin a human leg, which normally returns venous blood from the ankleupwardly through the leg, is anastomosed to the femoral artery at anupstream (proximal) location on the artery and a downstream (distal)location on the artery to assume the function of the femoral artery,i.e., to deliver arterial blood to the leg. Such a bypass procedure maybe required when the femoral artery has become too occluded or otherwiseimpaired between the upstream and downstream locations to transport theflow of blood required of it.

When the saphenous vein is to assume the function of the femoral artery,it becomes necessary to close off, i.e., to ligate, so-called "sidebranch" blood veins. These side branch veins are generally smaller thanthe saphenous vein and are colloquially known as "tributaries" when theylead to the saphenous vein and "perforators" when they lead to deepervenous circulation. Side branches ordinarily establish pathways forvenous blood into the saphenous vein for returning the blood to theheart and lungs. Accordingly, to prevent the unwanted flow of arterialblood directly into the venous system via the saphenous vein, the sidebranches and perforators must be ligated. Stated differently, byligating the side branches, arterial blood which is permitted to flowthrough the saphenous vein and thereby bypass the occluded segment ofthe artery is prevented from invading the venous system through the sidebranches.

Typically, side branches are ligated by constricting the side brancheswith sutures. Unfortunately, ligating side branches with sutures can betime-consuming and labor-intensive, because all the side branches mustbe located either by making a large number of small incisions in the legor by making one very large incision. Also, it is difficult to ligateside branches with sutures in less-invasive procedures, i.e.,endoscopically.

As recognized by the present invention, side branches of the saphenousvein may be ligated in less invasive procedures. More particularly, thepresent invention recognizes that blood flow through side branches ofthe saphenous vein can be quickly and easily stopped by advancing anelectrode into the side branch and energizing the electrode to cause thetissue to coagulate and thereby block fluid flow through the sidebranch. As further recognized by the present invention, varicose veinscan be quickly and easily treated by ligating them in less invasiveprocedures. Thereby, unsightly discolorations in the leg attributable tovaricose veins can be eliminated in an out-patient procedure.

Although coagulating devices have been introduced for other surgicalapplications, these devices typically have bulky components which aredesigned for use within a relatively large body cavity that has beenexposed by surgery. Consequently, existing coagulating devices cannoteasily be used to stop blood flow from "hard-to-reach" sources, such assaphenous vein side branches. Furthermore, existing coagulating devicescannot easily be used in less-invasive surgery for the treatment ofvaricose veins.

Moreover, many coagulating devices function simply by applyingelectricity to tissue. The length of time the tissue is exposed to theelectricity is controlled by the surgeon, usually by depressing a footpedal linked to a source of electricity, e.g., a Bovie model generatormade by Valley Labs of Colorado. Consequently, tissue can easily beunintentionally overheated, thereby causing unwanted scabbing, charring,and other unnecessary tissue damage. Such damage can be particularlyonerous in certain circumstances, e.g., saphenous vein side branchligation and varicose vein treatment. Indeed, excessive electro-ligationof varicose veins in an attempt to reduce discoloration caused by theveins may be a cure that is worse than the disease. Stated differently,applying rf energy to a blood vein over excessive time periods or atexcessively high power can result in arcing and perforation of vein.

It is therefore an object of the present invention to provide a devicethat can less-invasively ligate side branches of a saphenous vein.Another object of the present invention is to provide an apparatus andmethod for less invasive treatment of varicose veins. Still anotherobject of the present invention is to provide an apparatus and methodfor less invasive surgical ligation which is easy to use andcost-effective to manufacture.

SUMMARY OF THE INVENTION

A device for use in endoscopic surgery to inhibit blood flow through ablood vessel includes an elongated electrical conductor which has adistal end. Preferably, the conductor includes a segment that isbendable into a predetermined shape, and a direction indicator may beprovided for indicating the direction in which the conductor is bent.

A source of electricity is electrically connected to electricalconductor. As intended by the presently preferred embodiment, the sourceof electricity generates an rf output sufficient to cause the bloodvessel to collapse and insufficient to perforate the blood vessel. Also,an electrically insulative smooth flexible sheath surrounds at least asegment of the conductor. In accordance with the present invention, thesheath has an outside diameter of less than one millimeter (1 mm) topermit easily slidably engaging the sheath with the lumen of the bloodvessel.

An electrode is connected to the distal end of the electrical conductorsuch that the source of electricity can be energized to energize theelectrode to thereby cause the lumen of the blood vessel to collapsewhen the electrode is positioned in the vessel. In one presentlypreferred embodiment, the electrode extends beyond a distal end of thesheath, and the length of the electrode is approximately equal to thediameter of the blood vessel. Advantageously, the electrode is formedintegrally with the conductor, and the electrode includes a roundeddistal tip. Further, the electrode preferably includes an anti-stickingcoating which is deposited on the electrode.

Preferably, a feedback device is provided for sensing a preselectedparameter of the blood vessel. The feedback device generates a signalwhen the preselected parameter reaches a predetermined value, and thepreselected parameter is affected by the treatment of the preselectedportion of tissue. The preselected parameter can be temperature, inwhich case the feedback device includes a temperature sensor secured tothe apparatus for sensing the temperature of the electrode.

Alternatively, the preselected parameter is at least one electricalparameter selected from the group of parameters consisting of: source ofelectricity output voltage, time rate of change of source of electricityoutput voltage, source of electricity output power, time rate of changeof source of electricity output power, source of electricity outputcurrent, time rate of change of source of electricity output current,tissue electrical impedance, time rate of change of tissue electricalimpedance.

In another aspect of the present invention, an apparatus which isconnectable to a power source for electrically ligating a preselectedportion of tissue includes an electrically insulative sheath configuredfor slidably engaging a lumen of a body vessel. Additionally, theapparatus includes an electrode which is positioned in the sheath. Asintended by the present invention, the electrode is electricallyconnectable to the power source for energizing the preselected portionof tissue when the electrode is positioned adjacent the preselectedportion of tissue and the power source is activated to provide power tothe electrode. A feedback device is provided for sensing a preselectedparameter and for generating a signal representative of the magnitude ofthe preselected parameter. In accordance with the present invention, thepreselected parameter is affected when the preselected portion of tissueis energized by the electrode.

In still another aspect of the present invention, a method is disclosedfor treating a varicose vein. The method includes the steps of providingan electrically energizable electrode, and then percutaneously advancingthe electrode into the varicose vein such that the electrode isjuxtaposed with the wall of the varicose vein. Next, contact isestablished between the wall of the varicose vein and the electrode, andthe electrode is energized until the vein collapses around the electrodeto thereby block blood flow through the vein.

In yet another aspect of the present invention, a method is disclosedfor electro-ligation of a blood vessel. The method includes the steps ofproviding an electrically energizable electrode and an endoscopicinstrument, and disposing the electrode in the instrument. Then, theinstrument is percutaneously advanced with electrode into the bloodvessel, and the electrode is energized until the vessel collapses aroundthe electrode to thereby block blood flow through the vein.

The details of the present invention, both as to its construction andoperation, can best be understood in reference to the accompanyingdrawings, in which like numerals refer to like parts, and which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the apparatus for venous ligation of thepresent invention;

FIG. 2 is a cross-sectional view of the apparatus for venous ligation ofthe present invention, as seen along the line 2--2 in FIG. 1;

FIG. 3 is a block diagram of the electrical components of the apparatusshown in FIG. 1; and

FIG. 4 is a block diagram of the microprocessor logic for generating thecontrol signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring initially to FIG. 1, an endoscopic electrocauterizer forclosing off side branches of blood veins and for blocking blood flowthrough varicose veins is shown, generally designated 10. While thediscussion below focusses on side branch closure and varicose veintreatment, it is to be understood that the principles of the presentinvention disclosed below can be applied to a wide variety of medicaltreatments requiring tissue cauterization, including perforator veintreatment, hemorrhoid treatment, and neurosurgery applications.

As shown in FIG. 1, the cauterizer 10 includes a probe 11 and aconnector body 12. The connector 12 is preferably a standard banana plugconnector, and can be connected to a source 14 of electrical power viaan electrical line 16. The source 14 can advantageously be a Boviegenerator made by Valley Laboratories of Colorado.

It is to be understood that the probe 11 can be percutaneously advancedinto a blood vessel, e.g., a varicose vein, or that it could be engagedwith the lumen of an endoscopic surgery instrument 13, and then theinstrument 13 with probe 11 advanced into, e.g., the side branch of asaphenous vein. As intended by the present invention, the instrument 13can be any one of the instruments disclosed in the following U.S. patentapplications, all of which are assigned to the sole owner of theassignee of the present invention: Ser. No. 07/867,841, filed Apr. 13,1992 for an invention entitled "FLEXIBLE TIP CATHETER"; Ser. No.07/954,120, filed Sep. 29, 1992 for an invention entitled "FLEXIBLEENDOSCOPE WITH HYPOTUBE ACTIVATING WIRE"; and Ser. No. 07/970,402, filedNov. 2, 1992 for an invention entitled "ENDOSCOPE FOR SHUNT PLACEMENT",all of which are incorporated herein by reference.

In cross-reference to FIGS. 1 and 2, the probe 11 includes an elongatedelectrical conductor 18 having a cylindrically-shaped electrode 20formed integrally on the distal end of the conductor 18. Preferably, theconductor 18 has an electrical resistance below ten ohms per foot(10Ω/ft). In the preferred embodiment, the conductor 18 with electrode20 is made of type 304 stainless steel. By manufacturing the electrode20 integrally with the conductor 18, manufacturing costs of the probe 11are minimized, and a firm connection is established between theelectrode 20 and the conductor 18.

FIG. 2 shows that the conductor 18 has an outside diameter OD_(C1) ofabout eighteen thousandths of an inch (0.018"). Also, the conductor 18tapers radially inwardly to a bendable segment 22 having an outsidediameter OD_(C2) of about ten thousandths of an inch (0.010"). As theskilled artisan will appreciate, the bendable segment 22 is malleableand flexible. Consequently, the segment 22 can be bent into apredetermined curvilinear shape, as shown in FIG. 1, to facilitateadvancing the probe 11 into a side branch and to facilitate contactbetween the electrode 20 and the wall of a varicose vein into which theprobe 11 has been advanced.

As shown best in FIG. 2, the electrode 20 is formed with a roundeddistal tip 24. An abutment surface 26 is established by the electrode20, and the abutment surface 26 radially projects beyond the conductor18. Preferably, the electrode 20 has an outer diameter OD₁ of betweenabout twenty eight thousandths of an inch and eighty four thousandths ofan inch (0.028"-0.084"), and more preferably the outer diameter OD₁ isabout seven-tenths of a millimeter (0.7 mm).

The length L of the electrode 20 is between about one to ten millimeters(1-10 mm). Specifically, the length L is established to be approximatelyequal to the maximum diameter of the blood vein into which the probe 11is advanced. More specifically, for blood veins having a diameter ofabout four to six millimeters (4 mm-6 mm), the length L of the electrode20 is about four millimeters (4 mm). Also, for blood veins having adiameter of about six to eight millimeters (6 mm-8 mm), the length L isabout six millimeters (6 mm). Further, for blood veins having a diameterlarger than eight millimeters (8 mm), the length L is about eightmillimeters (8 mm).

In the presently preferred embodiment, a non-sticking, non-insulativesubstance 28 is deposited on the surface of the electrode 20 to inhibitsticking of the electrode 20 to body tissue during energization of theelectrode 20. Preferably, the substance 28 is chrome which is depositedon the electrode 20 by vapor deposition. Alternatively, the electrode 20can be coated with titanium nitrate or Teflon®.

FIG. 2 also shows that an insulative sheath 30 surrounds the conductor18 and abuts the abutment surface 26 of the electrode 20. As can be seenin FIG. 2, the outer surface of the sheath 30 is flush with the outersurface of the electrode 20. In accordance with the present invention,the sheath 30 is bonded to the conductor 18 with a high-temperatureepoxy.

As intended by the present invention, the sheath 30 is made of anelectrically resistive, smooth, biocompatible material, such as

PEBAX® made by Atochem, Inc. of New Jersey, or TFE Teflon®, whichtypically has a dielectric strength of about seven hundred to onethousand volts per mil of material (700-1000 v/mil). Also, the sheath 30is made of a material which will not easily melt or breakdown under thehigh temperatures that are typically generated during electrocautery.Further, the sheath 30 should be made of a material that has a lowcoefficient of friction.

PBax® is the presently preferred material of choice for the sheath 30 inlight of its above-mentioned attributes and because it is relativelyflexible, elastic, and has a low coefficient of friction. Theseattributes permit the sheath 30 to be easily advanced through apotentially curvilinear, small-diameter lumen of blood vein or anendoscopic instrument. Further to this end, the outside diameter OD ofthe sheath 30 (and, hence, the outside diameter of the probe 11) ispreferably equal to less than about one millimeter (1 mm). In onepresently preferred embodiment, the outside diameter OD of the sheath 30is between about twenty eight thousandths of an inch and ninety twothousandths of an inch (0.028"-0.092"). Alternative materials which canbe used for the sheath 30 include polyimide, polyethylene, andpolypropylene.

If desired, a sensor 32 (FIG. 1) can be attached to the electrode 20.The sensor 32 can be a thermocouple, thermistor, or other suitabletemperature-sensing device. Alternatively, the sensor 32 can be apressure sensor for sensing fluid pressure at the distal end of theprobe 11.

FIG. 2 shows that a flat, generally paralellepiped-shaped bend indicator34 is bonded to the sheath 30. As shown, the indicator 34 is formed witha projecting edge 36 that is distanced from the sheath 30. As intendedby the present invention, the bend indicator 34 is oriented duringmanufacturing such that the projecting edge 36 extends outwardly in thesame direction as the bend of the bendable segment 22 of the conductor18. The indicator 34 remains outside the patient's body during surgery,and the operator of the cauterizer 10 can consequently ascertain duringsurgery the direction in which the bendable segment 22 of the conductor18 has been bent.

FIG. 2 shows that the bend indicator 34 is formed integrally with ametal jacket 37, and the jacket 37 surrounds the sheath 30 to transmittorque to the probe 11. An insert 38 made of silicone rubber is disposedbetween the jacket 37 and sheath 30. Further, the probe 11 has aproximal end 39, and a high voltage line, including a high voltage lead40 and high voltage insulator 41, abuts the proximal end 39 of the probe11. A wire 42 is soldered to the high voltage lead 40 and conductor 18to further ensure electrical contact between the two components. It isto be appreciated that the high voltage lead 40 in turn is electricallyconnected to the source 14 of electricity via the line 16 and plug 12(FIG. 1).

In the operation of the cauterizer 10, reference is made to FIGS. 1 and2. The plug 12 is electrically connected to the source 14 ofelectricity. Thus, both the sensor 32 and electrode 20 of the probe 11are electrically connected to the source 14 of electricity.

The source 14 can be electrically connected to a microprocessor 44 whichis advantageously a type "486" microprocessor. As disclosed more fullybelow, the microprocessor 44 is electrically connected to the source 14,and the microprocessor 44 generates a control signal for controlling thesource 14 in response to, inter alia, signals from the sensor 32. Ifdesired, indicators 45 can be provided for displaying cauterizer 10voltage, current, impedance, temperature, and other parameters, inaccordance with the operation of the cauterizer 10 disclosed below.

Next, for side branch electro-ligation, the probe 11 is advanced intothe working channel lumen of the instrument 13. Then, the instrument 13into which the probe 11 has been advanced is itself advanced into theblood vein of a patient. The electrode 20 of the probe 11 can beselectively advanced out of the lumen in which it is slidably disposed,and the source 14 of electricity activated to electro-ligate a localizedportion of tissue. The probe 11 is then retracted from the vein of thepatient. As intended by the present invention, the power level of thesource 14 is sufficient to cause the vein to collapse, but insufficientto perforate the vein. To this end, when the source 14 is a Bovie modelgenerator, the so-called "cut" waveform (i.e., a 500KHz sinusoidal rfsignal) setting is used.

Alternatively, for varicose vein treatment, the probe 11 itself ispercutaneously advanced into the vein, and the wall of the vein ismanually urged against the electrode 20. Then, the electrode 20 isenergized to cause the wall of the vein to substantially collapseinwardly, thereby blocking blood flow through the vein. The electrode 20is then retrieved from the vein.

It is to be understood that while the cauterizer 10 disclosed above is amonopolar device, it may also be a bi-polar device, e.g., the cauterizer10 can have electrodes configured like those disclosed in co-pendingU.S. patent application Ser. No. 08/054,123, filed Apr. 26, 1993, for aninvention entitled "BiPolar Electrocauterizer", assigned to the soleowner of the present invention and incorporated herein by reference.

Now referring to FIG. 3, the electrical components of the cauterizer 10can be seen. As shown, the sensor 32 is connected to ananalog-to-digital ("A/D") converter 48, for converting the analogtemperature signal from the sensor 32 into a digitized signal. The A/Dconverter 48 can advantageously be a type AD57804P converter made byBurr Brown, or some other suitable converter known in the art.

FIG. 3 further shows that the A/D converter 48 is connected to a noisefilter 50. The noise filter 50 can be a hardware or, more preferably,software filter which filters noise from the digitized signal from thesensor 32. For example, the filter 50 can be programmed to discriminateagainst sixty Hertz (60 Hz) or fifty Hertz (50 Hz) noise from nearbyelectrical components. The filter 50 can also be programmed to average apredetermined number (e.g., ten) of consecutive signals from the sensor32 and output a signal representative of the average, or the filter 50can be a low-pass filter. When the noise filter 50 is a software filter,it can function by averaging a plurality (e.g., ten) of sensor signalsin accordance with means well-known in the art.

Also, the filter 50 can be programmed to block a signal from the sensor32 which greatly varies from the immediately previous signal. A greatvariance from one signal to the next may indicate an erroneous orspurious signal level. In other words, if a first signal from the sensorindicates an electrode 20 temperature of, e.g., eighty degreescentigrade (80° C.), and a second signal that is immediately temporallyafter the first indicates an electrode 20 temperature which varies bymore than a predetermined amount (e.g., 10° C.) from the first signal,the filter 50 blocks the second signal from further processing. Thehardware components, if any, of both the A/D converter 48 and the noisefilter 50 can be housed in the cauterizer 10 or source 14. When thefilter 50 is a software filter, the software filter 50 can be part ofthe microprocessor 44.

FIG. 3 also shows that a timer 52 is provided which monitors the lengthof time the source 14 energizes the electrode 20. The timer 52 generatesa signal representative of the length of time of electrode 20energization and sends this signal to the microprocessor 44. When thelength of time exceeds a predetermined time period, e.g., a time periodbetween about ten seconds and forty seconds (10 sec- 40 sec), themicroprocessor 44 causes the source 14 to stop energizing the electrode20.

Additionally, components are provided for measuring the output voltageand current of the source 14 of electricity, and for providing signalsrepresentative of the output voltage, current, power, and impedance(and, hence, the voltage, current, power, and tissue impedance at thetip of the electrode 20) to the microprocessor 44. More specifically, acomponent 54, e.g., a current sensing transformer or resistor, isconnected in series between the source 14 of electricity and theelectrode 20, and a current rectifier filter ("R/F") 56 samples thevoltage upstream and downstream of the component 54. Accordingly, thecurrent R/F 56 outputs a signal representative of the output current ofthe source 14 of electricity.

Also, a voltage sampling R/F 58 is provided for generating a signalrepresentative of the output voltage of the source 14 of electricity.Advantageously, both the current and voltage R/Fs 56, 58 can be fullwave diode rectifiers with associated filtering capacitors connected ina configuration well-known in the art.

FIG. 3 shows that the current and voltage R/Fs 56, 58 are respectivelyconnected to A/D converters 60, 62, each of which is substantiallysimilar to the temperature A/D converter 48. In turn, both A/Dconverters 60, 62 are connected to the microprocessor 44.

Still referring to FIG. 3, the microprocessor 44 generates an outputcontrol signal and sends the control signal to an electrical buffer 64.The buffer 64 is any suitable device which essentially isolates themicroprocessor 44 from the source 14 of electricity, and which providescorrect driving signals to the source 14.

The output signal from the buffer 64 is sent to the source 14 ofelectricity to control the output power of the source 14 of electricity.To do this, the control signal can be used to vary the output voltage ofthe source 14 of electricity, or the modulation of the signal from thesource 14 of electricity, by means well-known in the art. For example,the signal from the buffer 64 can be used as the bias signal to a powertransistor (not shown) that is part of the output circuitry of thesource 14 of electricity. Consequently, as the signal from the buffer 64changes, the bias of the transistor changes to change the output of thesource 14 of electricity.

Now referring to FIG. 4, the details of the operation of themicroprocessor 44 can be seen. The microprocessor 44 commences asampling cycle at begin circle 100. From the circle 100, themicroprocessor proceeds to block 102, wherein a software counter "T" isset equal to zero. Then at block 104, "T" is set equal to T+1. If, atblock 104, T equals a predetermined software counter "T₁ " themicroprocessor 44 stops i.e., exits the routine shown in FIG. 4.

Otherwise, the microprocessor 44 proceeds in parallel to decision blocks106, 108, and 110, and to blocks 112 and 114. At decision blocks 106,108, 110, the microprocessor 44 retrieves from memory and thenrespectively compares source 14 of electricity output voltage (V_(b)),electrode 20 temperature (T_(b)), and source 14 of electricity outputcurrent (I_(b)) to respective predetermined voltage, temperature, andcurrent setpoints V1, T1, I1. If either V_(b) or Tb exceeds itspredetermined setpoint, or if I_(b) falls below its predeterminedsetpoint, the microprocessor 44 generates a control signal to cause thesource 14 of electricity to stop energizing the electrode 20. Otherwise,the microprocessor 44 proceeds to blocks 116, 118.

At block 112, on the other hand, the microprocessor 44 calculates theimpedance (Z_(b)) of the tissue adjacent the electrode 20 by dividingV_(b) by I_(b). Then, the microprocessor 44 moves to decision block 120,where the microprocessor 44 compares Z_(b) to a predetermined setpointimpedance Z1. If Z_(b) exceeds Z1, poor electrical connection or poorplacement of the electrode 20 may be indicated. In such a case, themicroprocessor 44 generates a control signal to cause the source 14 ofelectricity to stop energizing the electrode 20. As intended by thepresent invention, the source 14 of electricity is deenergized beforeZ_(b) reaches zero (0). Else, the microprocessor 44 proceeds to blocks122 and 124. In the presently preferred embodiment, Z1 is set equal toabout fifty ohms.

It is to be understood that while overall impedance is used in thepresently preferred embodiment, the phase difference between V_(b) andI_(b) can be measured for determining the capacitive impedance componentand resistive impedance component, and then either impedance componentcan be used in lieu of or in addition to Z_(b). Indeed, the phasedifference between V_(b) and I_(b) can be used as an input to themicroprocessor 44 in lieu of or in addition to the parameters discussedabove.

Likewise, at block 114, the microprocessor 44 calculates the outputpower (P_(b)) of the source 14 of electricity by multiplying V_(b) andI_(b). Then, the microprocessor 44 moves to decision block 126, wherethe microprocessor 44 compares P_(b) to a predetermined setpoint powerP1. If P_(b) exceeds P1, the microprocessor 44 generates a controlsignal to cause the source 14 of electricity to stop energizing theelectrode 20. Otherwise, the microprocessor 44 proceeds to return block127, and thence back to block 104.

At blocks 116 and 118, the microprocessor 44 respectively calculates thedifference between V_(b), I_(b), and V_(b-1), I_(b-1) to yield ΔV, ΔI,where V_(b-1), I_(b-1), are the respective voltage and current valuescalculated in the immediately preceding cycle. Alternatively, V_(b-1),I_(b-1) can be averages of the n preceding corresponding values wheren=any integer, e.g., ten (10), three (3), etc.

From blocks 116, 118, the microprocessor 44 moves to respective decisionblocks 130, 132. At block 130, the microprocessor 44 compares ΔV to apredetermined voltage difference, i.e., ΔV₂. If ΔV exceeds ΔV₂, themicroprocessor 44 moves to block 134, wherein the microprocessor 44generates a control signal to cause the source 14 of electricity todeactivate or to reduce its power output by a predetermined incrementΔP, e.g., by two watts to four watts (2 w-4 w). Otherwise, themicroprocessor 44 moves to block 127 and thence back to block 104 foranother cycle.

Likewise, at block 132, the microprocessor 44 compares ΔI to apredetermined current difference, i.e., ΔI₂. If ΔI exceeds ΔI₂, themicroprocessor 44 moves to block 134, wherein the microprocessor 44generates a control signal to cause the source 14 of electricity toreduce its power output by ΔP. Otherwise, the microprocessor 44 moves toblock 127 and thence to block 104 for another cycle.

Recall that at block 120 the microprocessor 44 compared Z_(b) to apredetermined constant impedance setpoint Z1. As shown in FIG. 4starting at block 122, the microprocessor 44 also compares Z_(b) to avariable impedance setpoint Z2 which is patient-dependent.

More specifically, at block 122 the microprocessor 44 sets an enteringargument variable Z3 equal to Z_(b) if T equals a predeterminedstabilization time period T2. Otherwise, the entering argument variableZ3 is set equal to itself. More specifically, when T<T2, Z3 is set equalto a relatively low default value. When T=T2, Z3 is set equal to Z_(b),and when T>T2, Z3 remains equal to the value of Z_(b) set at T=T2. Thus,the entering argument Z3 is patient-dependent. In the preferredembodiment, T2 equals between about two (2) seconds to ten (10) seconds,and the default value of Z3 is equal to about two hundred ohms (200Ω).

Then, the microprocessor 44 moves to block 135, wherein themicroprocessor 44 retrieves a predetermined impedance limit Z2 byaccessing a data table and using Z3 as the entering argument. Arepresentative table is provided herein as Table 1. From block 135, themicroprocessor 44 moves to decision block 136, wherein Z_(b) is comparedto Z2. If Z_(b) exceeds Z2, the microprocessor 44 moves to block 134 toreduce source 14 of electricity output power or deenergize the electrode20 altogether, and thence to block 128 to generate a tone representativeof Z_(b). Otherwise, the microprocessor 44 moves directly to block 128to generate a tone representative of Z_(b). It is to be understood thatwhile block 128 in FIG. 4 indicates that a tone representative ofimpedance is generated, the tone or other tones could be generated whichare representative of the other parameters discussed herein. From block128, the microprocessor 44 moves to block 127 and then returns to block104.

The skilled artisan will appreciate that the operation of themicroprocessor 44 at block 122 ensures that the entering argumentvariable Z3 is set equal to a relatively stabilized Z_(b). Moreparticularly, for a brief initial stabilization period (T2), powerinterruption is avoided when minor transients in impedance (Z_(b)) mightoccur and otherwise cause the microprocessor 44 to deenergize the source14 of electricity. Stated differently, the microprocessor 44 reducessource 14 output power during the stabilization time T2 only in theinstance when Z_(b) is less than the initial default value of Z2, whichis accordingly set equal to a relatively low (e.g., eight hundred ohms(800Ω)) value.

On the other hand, after the stabilization period T2 elapses, Z_(b) canbe expected to reach a steady state value while the tissue surroundingthe probe 11 is treated by the electrode 36. During this treatmentperiod, the entering argument Z3 is defined to be equal to the value ofZ_(b) at time T=T2, and the table look-up of Z2 is thus accomplishedusing a patient-dependent entering argument Z3.

From block 124, the microprocessor 44 proceeds to decision block 138,wherein the microprocessor 44 compares ΔZ to a predetermined impedancedifference, i.e., ΔZ4. If ΔZ exceeds ΔZ4, the microprocessor 44 moves toblock 134, wherein the microprocessor 44 generates a control signal tocause the source 14 of electricity to reduce its power output by ΔP, andthence to block 127. Otherwise, the microprocessor 44 moves directly toblock 127, and thence to block 104 for another cycle.

Thus, at blocks 130, 132, 134 the microprocessor 44 determines whetherthe time rate of change of V_(b), I_(b), or Z_(b) are excessive, and ifso, the microprocessor 44 reduces the output power of the source 14 ofelectricity, or deenergizes the electrode 20 altogether. The presentinvention also envisions calculating the time rate of change oftemperature T_(b) in a like manner and reducing the output power of thesource 14 of electricity in response to an excessively rapid increase inT_(b) or in the time rate of change of T_(b).

The present invention contemplates the above-disclosed operation of themicroprocessor 44 because, as recognized by the present invention, thetissue impedance at the tip of the electrode 20, and the temperature ofthe tip of the electrode 20, is affected by the characteristics of thetissue immediately adjacent the electrode 20.

More particularly, when the tissue has not yet been cauterized, theimpedance at the electrode 20 tip is relatively low. In contrast, whenthe tissue has just undergone cauterization, the impedance at theelectrode 20 tip is relatively high. Thus, the output voltage, current,and impedance of the source 14 of electricity are all affected by thecauterization of tissue adjacent the electrode 20. Stated differently,the magnitudes of the output voltage and current of the source 14 ofelectricity, and the magnitude of the impedance of the tissue adjacentthe electrode 20, are dependent upon the body characteristics of thepatient. Likewise, the temperature (T_(b)) of the electrode 20 tip alsodepends in part upon the characteristics of the tissue adjacent the tipof the electrode 20.

Hence, by automatically controlling the output of the source 14 ofelectricity based upon any one of or a combination of Z_(b), I_(b),V_(b), P_(b), and T_(b) (and their respective time derivatives), thepresent invention ensures that tissue adjacent the venous wall is notdamaged any further than necessary to effect cauterization. Also, byprecisely controlling the output of the source 14 of electricity, thepresent invention ensures that tissue is precisely cauterized asappropriate for side branch/varicose vein closure. Alternatively, byautomatically generating a tone representative of any one of or acombination of Z_(b), I_(b), V_(b), P_(b), and T_(b) and theirrespective time derivatives, the present invention enables the surgeonto precisely control the source 14.

It is to be further understood that the present invention contemplatesestablishing power-dependent predetermined setpoints, i.e., setpointsthat vary with the manually-established power setting of the source 14of electricity. Thus, V1, I1, Z1, Z2, Z3, P1, T1, and ΔZ4 can all varywith the power setting of the source 14 of electricity. In such anembodiment, a data table correlating power setting with predeterminedsetpoints is stored in the electronic memory of the microprocessor 44for look-up by the microprocessor 44 at the appropriate decision blocksdiscussed above.

While the particular apparatus for venous ligation as herein shown anddescribed in detail is fully capable of attaining the above-describedobjects of the invention, it is to be understood that it is thepresently preferred embodiment of the present invention and is thusrepresentative of the subject matter which is broadly contemplated bythe present invention, that the scope of the present invention fullyencompasses other embodiments which may become obvious to those skilledin the art, and that the scope of the present invention is accordinglyto be limited by nothing other than the appended claims.

                  TABLE 1                                                         ______________________________________                                        Z3 (Ohms)     Z2 (Ohms)                                                       ______________________________________                                         0-49          0                                                              50-74         200                                                             75-99         225                                                             100-124       300                                                             125-149       350                                                             150-174       400                                                             175-199       425                                                             200-224       500                                                             225-249       550                                                             250-274       575                                                             275-299       600                                                             300-324       625                                                             325-349       650                                                             350-374       675                                                             375-449       700                                                             450-474       725                                                             475-499       750                                                             500-524       775                                                             525-549       800                                                             550-574       825                                                             575-599       850                                                             600-638       900                                                             ______________________________________                                    

What is claimed is:
 1. A method for treating a varicose vein, comprisingthe steps of:(a) providing an electrode; (b) percutaneously advancingthe electrode into the varicose vein such that the electrode isjuxtaposed with the wall of the varicose vein; (c) establishing contactbetween the wall of the varicose vein and the electrode by manuallypressing the vein; and (d) energizing the electrode until the veincollapses around the electrode to thereby block blood flow through thevein.
 2. The method of claim 1, wherein the electrode is energized by apower supply, and the method further comprises the step of determiningthe electrical impedance of the tissue adjacent the electrode.
 3. Themethod of claim 1, further comprising the step of automatically reducingenergization of the electrode when the impedance equals a predeterminedvalue.
 4. The method of claim 3, wherein the energizing step isaccomplished without perforating the vein.
 5. The method of claim 1,wherein the varicose vein defines a diameter of between about twomillimeters and eight millimeters (2 mm-8 mm), and the method furthercomprises of establishing the length of the electrode to beapproximately equal to the diameter of the varicose vein.